Aotus monkeys serve as the best animal model for the study of Plasmodium falciparum infections in man. Animals which are normally killed by infection with P. Falciparum will be identified by karyotype and immunized. The cellular and humoral aspects of the immune response of these animals will be studied. Sera from immune animals will be used in such procedures as cross-electrophoresis and immuno-electron microscopy, to identify parasite components to which the animals respond. Comparison of the results from animals having different levels of protective immunity will help determine those parasite components important in inducing protective immunity and those components which stimulate the immune response but play little or no role in providing protection. Forms of P. falciparum, grown in vitro in human red blood cells, will be isolated using a procedure recently developed in our laboratory. Biochemical tools including gel filtration, isoelectric focusing, electrophoresis, and affinity chromatography will be employed to isolate parasite components which can be used to protectively immunize monkeys. Those parasite components important in inducing immunologic protection against the parasite will be free of any cell antigens which might induce an autoimmune hemolytic anemia. The protective parasite antigens will be chemically characterized.